That maintenance requirement is just "keeping the cells alive when you're laying in bed in a coma" - actually using those muscles obviously requires more energy than that. Maintaining muscle mass is more than just a function of calories, though - in part because it's more expensive tissue, the body will try to make up caloric deficits from muscle before fat. Building and maintaining muscle requires that you keep your body in a state of muscle synthesis, which is itself a very metabolically-expensive process.
Numbers for energy/lb/day of muscle range from 6kcal-50kcal depending on who you're listening to, but the thing that everyone agrees on is that regardless of the number, muscle is multiple times more expensive than equivalent fat to maintain.